His face is that way because in the Handplates series and in regular Undertale he fell into the void, thus shattering him across time and space. This caused the world to forget about him in almost every respect, including physically

A mysterious character in the UNDERTALE universe. If you get a certain FUN value (random number at the start of the game) that you find in a mysterious gray room. Once you interact with him he disappears. This took the internet by storm and many fan comics (including this one) focus there stories around Gasters story. But that's just the basics. Research more if you want to learn more

Their are some people who think Alphys might actually be a Drake (a wingless dragon) the reasons why are interesting. Drake’s are known to live in dangerous places like in snowy wastelands or in Volcanoes, they also hoard knowledge instead of money which fits her being a scientist and that she collects manga and anime. Their are a few other reasons but I can’t remember them.